Schwerpunkte

E-mobility and autonomy

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11. Juni 2021, 08:43 Uhr   |  Irina Hübner

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© Zollner Elektronik | elektroniknet.de

For wireless charging: a coil system with field lines. The upper plate is integrated into the vehicle, the lower plate is a floor plate.

Charging electric cars today is often still cumbersome. Do e-car drivers really want to carry out the charging process manually, even in the age of autonomous vehicles? Researchers in the FEEDBACCAR joint project say no - they are relying on wireless charging and discharging.

If electric cars currently require a power connection, the charging cable will seem like a relic in a future of autonomous driving. After all, when the vehicle is on the road autonomously, it should also be able to master charging without human intervention. Researchers at the Institute for Automation and Communication (ifak) have therefore investigated how wireless charging and discharging of electric cars, i.e. inductive bidirectional charging, can be implemented in the future in the joint project FEEDBACCAR.

»We were able to show that not only wireless automatic charging of electric cars, but also feeding battery power from such vehicles back into the power grid are technically possible without any problems,« explains ifak project manager Axel Hoppe. Among other things, the project partners tested fully automatic battery charging and feeding charging current back into the power grid, even remotely. »With the support of radio solutions such as WLAN or, in the future, 5G, we were able to solve this optimally,« adds Hoppe.

The tests were carried out with a bidirectional inductive charging function up to 11 kW, which was integrated into the vehicle during the course of the project. "Both the high-voltage and for the communication infrastructure played well together in the process, according to Hoppe. ifak's project partners were car manufacturer Audi, supplier Zollner Elektronik and energy marketer e2m.

More than 90 percent system efficiency

»Contrary to what is often assumed, wireless charging is nearly as effective as conventional charging with a charging cable, because system efficiencies of more than 90 percent are achieved from the mains connection to the battery,« Hoppe says. The high efficiencies were achieved in part by the interoperable coil systems developed by the project partners as the basis for effective energy transfer.

During the course of the project, they tested various coil types and arrangements to assess their respective merits, for example in terms of compliance with international standards such as space requirements, thermal and electrical behavior, and efficiency. The selection of a suitable coil system is strongly dependent on the vehicle type and external requirements of the vehicle.

No viable business model for regenerative power so far

In addition, one aspect of FEEDBACCAR's research was to determine what business models would result for drivers or fleet operators if the energy were fed back into the grid. However, it became clear in the project that the current rules of the game in the electricity market are not yet sufficient to give a large number of mini-feeders, such as e-cars would be, an interesting opportunity in terms of price and with little bureaucracy.

For example, in its final report on the project, the energy service provider e2m does not currently see an economically viable business model solution for individual customers or energy service providers. Factors are, on the one hand, the insufficient revenue potential and, on the other hand, the necessary investments in hardware components.

In contrast, an electric car is attractive for homeowners with a photovoltaic system on the roof: In scenarios considered by FEEDBACCAR, the share of self-consumed solar power could be increased from 34 to 72 percent in households with a photovoltaic system. The highest shares of self-consumption were achieved when the vehicle was stationary a lot.

Solar system on four wheels extends range

A mobile solar system, on the other hand, is the basic idea behind the STREET research project, in which the Institute for Solar Energy Research Hameln (ISFH) is playing a major role. A small truck with solar power modules on the roof and on the side paneling covering a total area of 15 m² was developed. The electricity produced by the special modules can be used directly by the e-delivery vehicle.

ISFH expects the small truck, a Streetscooter, to have an annual range extension of about 5200 km for trips in Lower Saxony and significantly more in more southern regions by using the solar power on the body. According to ISFH, the technology developed in Europe not only enables the greatest possible cell and module efficiencies, but also high module yields due to a lower temperature coefficient. »Autonomous driving, as we all know, means driverless. But it can also be understood figuratively as greater independence. We are already achieving this today with the STREET demonstrator,« explains project coordinator Prof. Robby Peibst.

E-vehicles become more interesting for the electricity market

»As the auto industry switches to e-vehicles, the amount of electricity needed to run the cars increases, despite their great efficiency in converting energy. This makes the cars interesting for the electricity market, which is increasingly dominated by wind and solar energy. Institutes of the Zuse community are successfully working on technical solutions to integrate cars into the electricity market and reduce their climate gas emissions,« explains the managing director of the Zuse community, Dr. Klaus Jansen.

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Zollner Elektronik AG, ifak e.V. Magdeburg, ifak system GmbH, Audi AG